1. Technical Field
The present invention relates to an oscillation device and a timepiece with temperature compensation function.
2. Related Art
As a timepiece having such high accuracy as that of an “annual equation” timepiece, there has been known a timepiece with temperature compensation function for correcting the temperature characteristic of a quartz crystal oscillation circuit for outputting a time reference signal (see, e.g., JP-B-6-31731 (Document 1)). Further, there has also been known an oscillation circuit equipped with a frequency adjustment mechanism for adjusting the frequency of the oscillation signal of a quartz crystal oscillation circuit (see, e.g., JP-A-2008-244617 (Document 2)).
In Document 1 and Document 2, load capacitances to be connected to both ends of the quartz crystal resonator and a power supply are switched by control using data written to a nonvolatile memory such as an electrically erasable programmable read-only memory (EEPROM) or a programmable ROM (PROM) or a control signal from a control circuit incorporated in an IC to change the capacitance to thereby change the oscillation frequency.
However, the data from the EEPROM, the PROM, or the like and the control signal from the control circuit are not a signal in a constant voltage level. Therefore, due to a variation of the power supply voltage, the control signal input to a switch or a transmission gate configured using a MOSFET (metal-oxide-semiconductor field-effect transistor) varies.
Since the control signal is applied to the gate of the switch or the transmission gate formed of the MOSFET, the flowability of a current varies due to the variation of the voltage. If the flowability of the current in the switch or the transmission gate varies, there arises a problem that the time for charging the capacitance for adjusting the oscillation frequency varies, and thus, the oscillation frequency varies.